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Interpretive Summary: Root-knot nematodes are important pests of peach in the U.S. and other parts of the world if not controlled. Meloidogyne incognita and M. javanica are the predominant species on peach. Recent reports indicated that the newly released Guardian rootstock was resistant to Meloidogyne incognita (GA peach isolate) and M. javanica (NC-tobacco isolate). Evaluating different root-knot nematode isolates of M. incognita and M. javanica and other Meloidogyne spp. is important in determining just how broad and effective Guardian's resistance is. Greenhouse studies were initiated to examine the susceptibility of Guardian rootstock to two different root-knot nematode populations, M. javanica from California and a Meloidogyne sp. from Florida. The M. javanica (CA-isolate) is known to parasitize S-37 peach rootstock; whereas, Meloidogyne sp. (FL isolate) is known to reproduce on Nemaguard. These nematode populations were of particular interest because both S-37 and Nemaguard are in the pedigree of Guardian. Current studies indicate that Guardian was a moderate host to M. javanica (CA isolate) and a good host to Meloidogyne sp. (FL-isolate). These data provide useful insights into the potential utilization of Guardian rootstock in peach orchards infested with root-knot nematode. Furthermore, it is important to know the parasitic nature of the nematode isolate one is using when evaluating Prunus rootstocks for resistance to root-knot nematode in order to ensure accurate results.

Technical Abstract: Guardian peach rootstock was evaluated for susceptibility to Meloidogyne javanica (California-isolate) and Meloidogyne sp. (Florida-isolate) in the greenhouse. The Meloidogyne sp.(FL isolate) has an atypical esterase pattern and is presently uncharacterized. Furthermore, M. javanica (CA-isolate) is known to parasitize S-37 peach rootstock; whereas, Meloidogyne sp. (FL isolate) is known to reproduce on Nemaguard peach rootstock. These nematode populations were of particular interest because both S-37 and Nemaguard are in the pedigree of Guardian. Nematode reproduction was determined by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root. Results indicate that Guardian rootstock appears to be moderately susceptible to M. javanica (CA-isolate), but deemed susceptible to Meloidogyne sp (FL isolate).